Subscriber&#39;s station for carrier frequency communication systems



Sept. 28, 1943. H. NlTZ 2,330,612

SUBSCRIBERS STATION FOR CARRIER FREQUENCY COMMUNICATION SYSTEMS Filed Nov. 27, 1940 7 JUUU U C M Fig.7

/nventor:

Ilerbert M75 Patented Sept. 28, 1943 SUBSCRIBERS l2,s3o,s12 a V STATION FOR panama FREQUENCY GOMIWUNICATION SYSTEMSv Herbert Nita Berlin, Germany; vestedv in. the

, AlienPlfoperty Custodian,

ApplicationNovember 27, 1940; Serial No. 7 InIGermany December. 8,1939

Telephone systems are known which have means for switching subscribers stations to a carrier frequency four-wire terminal circuit, one

direction of traific, preferably from the exchange to the subscriber, being effected in carrier frequency fashion while the other, preferably from the subscriber to the exchange, is in low frequency fashion.

It has been proposed in such systems that at the subscribers station the microphone be removed from the usual bridge connection and connected directly across the line. Such arrangement has the advantage that the four-wire operation is free from the attenuation caused by the bridge connection.

According to the present invention, in order further to improve the mode of establishing connections originated from the transmitting side, a repeater coil or transformer which allows unidirectional currents to pass through it is employed for connecting the microphone to the line, whereby the alternating current resistance of the microphone is matched to the line.

In the accompanying drawing, Fig. 1 is a diagram showing one embodiment of the invention, while Fig. 2 is a diagram representing a modification of this embodiment.

Referring first to Fig. 1, l and 2 are terminals over which the subscribers station circuit is connected to the subscribers line. B is the usual bridging repeater coil, the secondary winding of which is connected to the receiver over terminals 3 and 4 for ordinary two-wire operation. When the subscriber's station is connected to a fourwire terminal circuit and carrier frequencies are used for the direction of trafiic from the exchange to the subscriber the coil B is not used the receiver being connected in known manner to the terminals I and 2 over a demodulator and a highpass filter.

According to the invention, the microphone M is coupled to the line by an additional matching repeater coil or transformer U having split primary and secondary windings the halves of both windings being connected together over a common condenser C. Thus the direct current supplied from the line for feeding the microphone M flows from line terminal I over the upper half of the primary winding of transformer U and the upper half of the secondary winding to the microphone M and thence over the lower halves of the secondary and primary windings to the line terminal 2. The alternating current component, however, flows through the two halves of the secondary and primary windings interconnected in series by the condenser C and .the transformer Uithus actstoxmatch the alternating current resistance of the microphone M to the line.

In the modification shown in Fig. 2, the repeater coils U and B of Fig. 1 are combined in a single three-winding transformer B in such manner that in the normal two-wire circuit this transformer acts as a. bridging transformer whereas in the carrier frequency four-wire circuit it acts as a matching transformer which at the same time permits direct current to flow to the microphone M. Switch contacts 2' are provided for converting the subscribers substation circuit alternatively either fornormal two-wire working or for use with a carrier frequency fourwire terminal, the contacts being shown in the position for the last-mentioned method of operation. I

With the upper contacts 2' closed, the centre winding 0', d and the right-hand winding of the repeater coil or transformer B are connected in :a bridge connection for two-wire operation, the resistance R being connected in series with the line and serving for bridge balance andthe microphone M being connected between line terminal I and the upper end of the lower half of the centre winding 0, d. The receiver is connected to terminals 3 and 4.

With the lower contacts i closed, the lefthand winding and the centre winding 0', d of the transformer B function as a repeater coil to couple the microphone M to the line for operation with a four-wire terminal in the same manner as the transformer U of Fig. 1. The righthand winding is not used, the receiver being connected to line over a demodulator and highpass filter. The additional portion 0, c of the centre winding is arranged tobe connected in circuit when the upper contacts 2' are closed for two-wire operation. This is for the purpose of obtaining a correct impedance match in the two switching positions, that is, in the position for normal two-wire operation, between the line and the telephone receiver, and in the position for carrier frequency operation between the line and the microphone.

The novel arrangement as compared with arrangements having the microphone coupled directly to the line acts to decrease the attenuation by about 2.6 decibels.

What is claimed is:

1. In a telephone system, a subscribers line and a subscribers station circuit comprising a microphone and a transformer for coupling said microphone to said subscribers line, said transformer having split primary and secondary windings, connections between one end of each half of said split primary winding and the said subscribers line, connections between one end of each half of said split secondary winding and said microphone, and a condenser connected between the other ends of the two halves of the said primary winding and the other two halves of the said secondary winding.

ends of the '2. A subscribers station circuit according to claim 1, further comprising a receiver, a tertiary winding on said transformer for. coupling said i receiver to said subscribers line, additional turns on said primary winding, and'switching means for connecting said primary winding across said subscribers line with or without said additional turns in circuit for the purpose of effecting an impedance match between said receiver and said line or between said microphone and said line asidesired'.

I 31in a. telephone system, a subscribersrline 20 saidmicrophone and said line and a subscribers station circuit comprising a microphone and a transformer for coupling said microphone to said subscribers line, said transformer having split primary and secondary windings, connections bet-ween one end of each half of said split primary winding and the said subscribers line, connections between one end of each half of said split secondary winding and said microphone, and a condenser interconnecting the two halves of the said primary winding and the two halves of the said secondary winding, a receiver, a tertiary winding on said transformer for coupling. said receiver to said subscriber's line, additional turns on said primary winding, and switching means for connecting said primary winding across said subscribers line with .or without said additional turns in circuit for the purpose of efiectmg an impedance match between said receiver and said line or between as desired.

HERBERT NITZ. 

